Experimental Study On Surfactant Flooding In H Reservoir In Xinjiang Oilfield

The H reservoir of Xinjiang oilfield is the typical low-permeability reservoir,while there exists a serious problem that the effect of water injection is poor due to the oil layer's inhomogeneity.Thus,the surfactant flooding experiment was carried out to test the performance and applicability.Two kinds of surfactants,KPS-5+YF-11(1:1)and YF-12,were selected through extensive screening evaluations,which formed super-low interfacial tension with the crude oil of H reservoir of xinjiang oilfield.The interfacial tension reached 10-4mN/m when the mass concentration of the two surfactants were 0.2%.The 3 months aging test demonstrated that the interfacial stable ability of combined systems was better than that of YF-12 system for the interfacial tension kept at 3.9×10-3mN/m.Then,the emulsifying property and the altering wettability to rock surface of the two systems were respectively studied under reservoir condition.The results showed that the combined system was easily emulsifying under the dynamic condition and stratifying under the static condition,while YF-12 presented preferable emulsifying stability;In the low concentration range,the surfactant concentration had little effect on the type of emulsion,the smaller the oil-water ratio,the easier it was to form O/W emulsion;The combined system showed superior matching with the formation porosity,for the emulsion droplet diameter of 4?m was smaller than that of YF-12.In addition,the combined systems has better wettability improvement on rock surface than YF-12 system,which could change the rock surface from oil wetting to water wetting,the wetting angle of the reservoir rock in the complex system was reduced by 48.3°after 10 days.The static adsorption and dynamic adsorption experiments on the natural cores of the combined systems showed that the dynamic adsorption value on the rocks was below 0.5 mg/g,less than the static adsorption capacity.Through the research on property of surfactant flooding,KPS-5+YF-11 combined systems were determined to be the object oil-displacement agent for Xinjiang oil field.The laboratory core physical simulation experiment showed that the lower the interfacial tension was,the higher the oil recovery and the grater the depressurization rate will be;Under the homogeneous cores conditions,the optimal injection rate was 0.3ml/min,the slug volume was 0.5PV;The sooner the injection timing,the better the oil displacement efficiency;With the increase of rock permeability,the oil displacement efficiency increased first and then decreased,when the core permeability was less than 34.15×10-3?m2,the oil displacement efficiency was better;In the reservoir conditions,the natural core flooding experiment was conducted with the optimal injiection way of combined system demonstrated that the oil recovery could be 68.1%which was improved 16.5%,and the depressurization rate reached 32.5%.The greater permeability differential under the heterogeneous condition,the poorner the oil displacement efficiency,while the injection time had non-influence to recovery rate.In the reservoir conditions,the three parallel natural cores flooding experiment was conducted with the optimal injiection way of combined system suggested that the type of emulsion was O/W,the recovery efficiency was 62.5%which was enhanced to 27.8%,and depressurization rate was 39.7%.KPS-5+YF-11 combined system formed super-low interfacial tension with crude oil of H reservoir in XinJiang oilfield,which showed preferable emulsion performance,could improve the wettability of rock surface and decrease the adsorption loss.It also provided the effect of pressure decreasing and oil output increasing.Therefore,the combined system has practical significance for the development of XinJiang oilfield.